Stackable block



FIG. 1 is a perspective view of a stackable block showing my new design;

FIG. 2 is a right side view of the stackable block;

FIG. 3 is a top view of the stackable block;

FIG. 4 is a left side view of the stackable block;

FIG. 5 is a bottom view of the stackable block;

FIG. 6 is a rear plan view of the stackable block; and,

FIG. 7 is a front plan view of the stackable block.

The broken lines in FIG. 1 represent the bounds of the claim and all other broken lines represent portions of the article that form not part of the claimed design. None of the broken lines form a part of the claimed design. 

CLAIM The ornamental design for a stackable block, as shown and described. 